The kingpin (Kingpin) is the center of rotation of the steering wheel of a conventional car, and is a thicker pin. Now, many independent suspension cars have no main sales. However, in the wheel positioning, the term "master pin" is still used as a synonym for the steering axis of the steering wheel. It is considered that the steering wheel is rotated to the left and right with the kingpin as the axis when turning.

The so-called kingpin tilting is to tilt the upper end of the kingpin (ie, the steering axis) slightly rearward. Viewed from the side of the car, the main pin axis forms an angle with the vertical line passing through the center of the front wheel, that is, the caster caster angle.

The role of the kingpin rearward tilt is to increase the stability of the car when driving straight and to automatically return the front wheel after steering.